Using Growth-Based Models to Study Behavioral Factors Affecting Sexual Size Dimorphism

Abstract

In animals with asymptotic growth after maturity, a variety of factors can lead to inter- and intraspecific variation in sexual size dimorphism (SSD). Growth-based models tailored for a particular taxon provide a useful framework for analyzing questions about the proximate bases, adaptive significance, and evolution of SSD. This paper shows how growth-based models designed for Anolis lizards have been used to study the effects of male territorial and competitive behavior on SSD and adult size distributions. In a comparative study of different species of anoles, indices of SSD based on male and female asymptotic snout-vent length (SVL) have been used to confirm a prediction from territorial theory that SSD should be related to inter-female distance. Within populations of Anolis sagrei and Anolis limifrons, adult size distributions were sometimes skewed in favor of larger males than predicted by null growth-based models, as a result of the underrepresentation of small, young males in samples containing females of the same age. A relative shortage of newly mature males in adult size distributions is consistent with behavioral studies suggesting that young, small males may bear the brunt of aggression from larger territorial males. Hence, growth-based models can be used to suggest and test behavioral and other hypotheses about the factors affecting SSD.